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INA 125 simple circuit diagram

Other Parts Discussed in Thread: INA125

dear sir,

i want to test INA125 instumentaion amplifier with single ended supply .same as data sheet ,But we have no load cell.the power supply volt 12v

we connect simply another source ranging 1 mv to 5v instead of load cell across vin+ and vin-.

+ voltage connected to V+ and ground of source connected to v-.then we shorted the power supply ground to source ground

that is v- iand iaref   is ground and  v+ just say .1v then difference become .1v

but the output not good.gain is very low than actual gain lets say if .1 v i get only .5v. lower gain.and also gain not consistent.

if we off the source supply the output become 11 v.

we got reference supply 10v.please help us what is the problem.

  • Lijo,

    If you could draw a schematic of your circuit and attach it to this thread it would greatly help us support you. 

    I believe the issue you are having is that your input signal has a common mode voltage of 0V and you are operating the INA125 on a single supply (negative power supply connected to ground). This configuration violates the input common mode voltage range of the INA125. There is a curve in the datasheet which indicates that this configuration will be a problem:

    Notice in the region for a single +5V supply the output voltages that the INA125 is able to produce range only from a little less than 1V to a little more than 4V. In your configuration the output is trying to go to 0V and is saturated at its negative supply rail. You can either add a negative power supply voltage to the INA125, or center the input common mode voltage and reference voltage at the mid-supply point.

  •  sir we didnt get proper result how can i test  ina 125 without load cell.how can test ina 125.we working in research and development company .we are working under project .so please how to get proper gain without load cell.what is the problem in the circuit.

  • Lijo,
    Please keep posts on this issue to a single thread. As both Thomas Kuehl and I have stated in our responses you cannot have the negative supply, input common mode voltage, and output reference voltage all at 0V. You have 2 options:

    Option 1: Use a negative power supply. Connect pin 3 to a negative voltage. Even a voltage as small as -1V is probably enough to bring the output of the INA125 out of saturation. You could also use symmetrical supplies like +/-12V.

    Option 2: Connect a reference voltage to the IA ref (pin 5) , a voltage greater than 1V should be sufficient. And connect a voltage source between pin 7 and ground to increase the input common mode voltage.